Recently, distortion-compensation amplifiers for reducing distortions in base stations, which are used in base station wireless apparatus such as of mobile communication systems or the like, employ a delay line for the purposes of detecting and suppressing distortions.
As shown in FIG. 27, for example, a delay line 200 includes a bandpass filter 208 having an input terminal 202, an output terminal 204, and a plurality of resonators 206A through 206I. The input terminal 202 and the resonator 206A in the first stage are connected to each other by a capacitor C1, and the output terminal 204 and the resonator 206I in the final stage are connected to each other by a capacitor C2. The resonators 206A through 206I are connected by capacitors C3 through C10.
Heretofore, as shown in FIG. 28, there has been known a delay line 210 that is similar to the delay line 200 shown in FIG. 27, in which a skipping circuit 212 is connected parallel to coupling capacitors C3 through C8 between adjacent resonators 206A through 206G and has a plurality of coupling capacitors C9 through C19 (see, for example, Patent Document 1), and, as shown in FIG. 29, there has been known a delay line 300 in which a skipping circuit 302 is connected parallel to coupling capacitors C1 through C6 between adjacent resonators 206A through 206E and has coupling capacitors C7 through C10 and inductors L1 through L7 (see, for example, Patent Document 2).
The examples shown in FIGS. 28 and 29 are advantageous in that the flatness of the group delay time in the passband of the bandpass filter 208 can be maintained and the group delay time deviation can be reduced without involving an increase in the number of resonator stages.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-257505    Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-273661